Performance of a sand filter in removal of algal bloom for SWRO pre-treatment

Abstract

The present study has two main purposes: to investigate the performance of a first-stage sand media filter in a case of several reconstituted algal blooms and to better understand fouling mechanism of sand filter due to micro-algae. The retention efficiency of the filter obtained for 30,000, 50,000 and 145,000 cells/ml alga suspensions of Chlorella vulgaris is respectively above 90, 90 and 80% only during the first hours of filtration and drop at 74, 78 and 48% after 7 h. The fouling investigation reveals that the number of micro-algae captured in the filter is much higher in the first 30 cm of the bed. The ratio between the volume occupied by micro-algae retained in the filter and the total pore volume does not exceed 0.015% and suggests a minor effect of straining filtration mechanism. The effect of the micro-algae size (C. vulgaris (2–8 μm) and Heterocapsa triquetra (17–18 μm)) seems not to have a significant impact on the retention efficiency which is encouraging the idea that the adsorption mechanism has a higher affect on the retention than the straining filtration.

Keywords:

• Sand media filter
• Algal bloom
• Seawater pre-treatment
• Fouling mechanism

Acknowledgement

Specials thanks to Thi-Dong-Phuong NGUYEN and Antoine SOULIES for providing Chlorella vulgaris culture samples.

Notes

Presented at the International Conference on Desalination for the Environment, Clean Water and Energy, European Desalination Society, 23–26 April 2012, Barcelona, Spain